Fields that probably should not be (such as X-fledge-bidding-signals-format-version)

[martinthomson]

Signaling content version information in HTTP headers is not generally recommended. A more generally acceptable approach is to use content types. Using content types allows for version negotiation with Accept fields in the request.

For instance, the response could use application/protected-audience-kv+json or something along those lines.

If there is a need to make a breaking change to the format, a new content type can be minted. They are cheap.

See also RFC 6648.

[JensenPaul]

We agree that X-fledge-bidding-signals-format-version is not a particularly ergonomic mechanism, but rather than graduate it to a content type, we were planning to simply deprecate and remove it as it was meant to only be temporary; see comment here: #772 (comment)

[martinthomson]

Add the following to the list of fields that probably should not be fields: X-kv-query-request-version, x-kv-query-response-version, data-version.

[peiwenhu]

X-kv-query-request-version and x-kv-query-response-version are intended for things that will stick for longer so we'll take it as a work item to use content-type instead.